The Extended Cycle of Solar Activity and the Sun’s 22-Year Magnetic Cycle

Abstract

The Sun has two characteristic migrations of surface features---the equatorward movement of sunspots and the poleward movement of high-latitude prominences. The first of these migrations is a defining aspect of the 11-yr Schwabe cycle and the second is a tracer of the process that culminates in solar polarity reversal, signaling the onset of the 22-yr magnetic cycle on the Sun. Zonal flows (torsional oscillations of the Sun's differential rotation) have been identified for both of these migrations. Helioseismology observations of these zonal flows provide support for the extended (>11-yr cycle) of solar activity and offer promise of a long-term precursor for predicting the amplitude of the Schwabe cycle. We review the growth of observational evidence for the extended and 22-yr magnetic cycles and discuss: (1) the significance of latitude ∼50∘ on the Sun; (2) the ``over-extended'' cycle; and (3) the outlook for solar cycle 25.